Re: [patch 2/2] KVM: x86: add option to advance tscdeadline hrtimer expiration

Paolo Bonzini
2014-12-11T18:58:52Z

On 11/12/2014 04:07, Marcelo Tosatti wrote:
>> > So, on APICv, if the interrupt is in PIR but it has bits 7:4 <=
>> > PPR[7:4], you have a problem. :( There is no APICv hook that lets you
>> > get a vmexit when the PPR becomes low enough.
> Well, you simply exit earlier and busy spin for VM-exit
> time.

Okay, given how small the jitter is in your plots, a small busy wait is
not the end of the world even if it caused a very short priority
inversion. Can you add a tracepoint that triggers when you do the busy
wait, and possibly a kvm stat that counts good (no busy wait) vs. bad
(busy wait) invocations of wait_lapic_expire?

Thanks,

Paolo